Apparatus for driving and/or extracting piles

ABSTRACT

A method and apparatus for the vibratory driving of piles in which a hydraulic cylinder-and-ram assembly is arranged to impart a vibration of asymmetric waveform to the pile. The apparatus includes a closed-loop servo control system by which the movement of the ram relative to the cylinder is according to an input signal of the desired waveform.

United States Patent 3,650,335 Lee et al. Mar. 21, 1972 [54] APPARATUS FOR DRIVING AND/OR References Cited EXTRACTING FILES UNITED STATES PATENTS I 1 inventors: Norman Coventry; Franck ni 3,371,726 3/1968 Bouyoucos ..l75/56 Levems, Abmsdon, both of England 2,931,388 4/1960 Renick et al.... ..91/39 73 Assignee: Keelavite Hydraulics Limited, Allesley 2,955,460 1960 Stevens BI 31. ..91/ Coventry, warwickshire, England 2,965,076 12/1960 Zelsloft ..9l/40 3,054,463 9/1962 Bodine ....l/l9 Flledl 1959 3,262,507 7/1966 Hansen ....l75/56 2 AppL 864 7 1 3,411,592 11/1968 Montabert ..173/137 Primary Examiner.lames A. Leppink [301 Fowl! Applicauon Priority Data Attorney-Watson, Cole, Grindle & Watson Oct. 11, 1968 Great Britain ..48,337/68 Y [57] ABSTRACT [52] U.S.C1 ..l73 /9l,9l/40, 117734112352, A method and apparatus for the vibratory driving of piles in Eon! 00 which a hydraulic cylinder-and-ram assembly is arranged to impart a vibration of asymmetric waveform to the pile. The [5 1 0 "/19 apparatus includes a closed-loop servo control system by which the movement of the ram relative to the cylinder is ac cording to an input signal of the desired waveform.

6 Claims, 5 Drawing Figures Patented March 21, 19:12 3,650,335

2 Sheets-Sheet 1 INVENTORS Human Ln IQaucus Ltve'rus BY ME; X4331! W343 ATTORNEY This invention relates to apparatus for driving and/or extracting piles. For convenience the remainder of this specification will refer only to the driving of piles, but it will be appreciated that, by suitable adaption of the mode of operation or the attitude of the apparatus, the apparatus may be used for extracting piles.

Various means for driving piles have hitherto been used. The conventional method is to raise a weight by means of a winch and allow the weight to drop onto the upper end of the pile. Steam hammers have also been used which deliver to the upper end of the pile successive blows with a frequency considerably in excess of that obtainable with the traditional winch pile driver. More recently there has been some investigation into the possibility of driving piles by means of vibration. By this method the pile is given a vibration of a frequency which is high compared with that hitherto used for pile driving and is in the range of 25 to 150 cycles per second. It is found that when the pile is vibrated at this frequency the cohesion and/or friction of the soil in contact with the pile is reduced considerably and the pile moves into the earth as though through a viscous medium. In one form of apparatus described in British Pat. No. 1,057,248 the pile is stated to descend under the weight of the pile-driving apparatus which may be several tons in addition to the weight of the pile itself. With this apparatus the vibration is produced by a double acting hydraulic ram of symmetrical construction, pressurized hydraulic fluid being applied to opposite sides of the ram alternately.

According to one aspect of the present invention in a method of driving a pile by applying a vibratory force to the pile longitudinally of the pile, the force has a nonsymmetrical waveform, i.e. the magnitude of the force increases at a different rate in one direction compared with that in the opposite direction. it is believed that by using an asymmetrical vibration forces may be imparted to the pile which assist in driving it in the desired direction. With the previous arrangement the force of vibration has tended to move the pile as much in the opposite direction as in the desired direction and movement of the pile has been produced largely by the applied weight. By the present method the vibratory force is used so that there is an actual driving effect as well as a vibratory effect and the energy is used more efficiently. Put another way, the previous arrangement imparted a force which varied sinusoidally whereas with the present method it is possible to impart a series of more or less sharp blows to the pile in one direction only, the forces in the opposite direction being smoother and of less magnitude. In practice it may be found that vibrations of different waveforms suit different conditions.

The invention also includes, according to asecond aspect, apparatus for performing the method. Thus, according to this aspect, vibratory pile-driving apparatus comprises a mass adapted to be connected to a pile and to be movable longitudinally thereof and motor means arranged to reciprocate the mass relative to the pile longitudinally thereof to impart vibratory forces to the pile, the motor means being arranged to impart or being adjustable to impart to the pile forces of nonsymmetrical waveform.

The motor means may be of various forms, e.g. electrical or pneumatic, but preferably comprises a double acting hydraulic cylinder-and-ram assembly, one of the two moving elements of the assembly having means of connection to a pile, and valve means for controlling the supply of pressurised working fluid to and from the working chambers of the assembly, the valve means being arranged so as to control the supply of fluid that the acceleration of the movement of the ram in one direction relative to the cylinder is or can be caused to be greater than in the opposite direction.

The difference in acceleration may be produced in various ways. For example, the valve means may be arranged to supply fluid to a piston area for movement of the ram in one direction which is different from the piston area supplied for movement in the opposite direction. On the other hand, the piston may have surfacesof equal area facing in the opposite directions and the valve means is arranged to supply fluid to the areas facing in opposite directions at different rates. This may be done by connecting the oppositely facing areas to fluid supplies at different pressures as from two different pumps but this is not necessary and the valve means may be arranged to supply from a common fluid supply at different rates. In the preferred arrangement, there is a servovalve for controlling the supply of pressurized working fluid to andfrom the working chambers of the assembly, actuating means for the servovalve and a closed loop control system comprising a position transducer arranged to provide a measured value signal representing the instantaneous position of the ram relative to the cylinder, means for supplying an input signal of asymmetric waveform, means for comparing the measured value signal with the input signal and for delivering a command signal dependent upon the deviation determined by the comparison, and means for supplying the command signal to the actuating means.

The invention may be carried into practice in various ways and two vibratory pile drivers will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a vertical longitudinal section through the firstpile driver;

FIG. 2 is a plan view of the pile driver shown in FIG. 1;

FIG. 3 is a diagrammatic representation of the servovalve housed in the pile driver;

FIG. 4 is a block diagram showing the control system of the pile driver; and

FIG. 5 is a much simplified longitudinal section similar to FIG. 1 of a second form of pile driver.

The pile driver shown in FIGS; 1 and 2 comprises a massive body 1 which guides a massive piston rod 2. The lower end of the piston rod is formed with a disc-shaped foot 3 to which the pile to be driven is connected by a ring of bolts 4. Secured to the upper end of the body 1 by tie rods 10 is a cylinder 5 having a stepped bore, the lower part 6 of which constitutes the actual cylinder chamber. At the upper end, the piston rod 2 has a reduced diameter portion 7 to which a sleeve 1 l is secured by a retaining ring 8 and bolts 9. The external surface of the sleeve 11 has a step or shoulder 12 and thus has a first portion 13 of larger diameter which forms the piston itself and a portion 14 of lesser diameter which is of the same diameter as the part of the piston rod 2 below the piston and is guided within the upper part of the bore in the cylinder 5. The lower part 6 of the cylinder includes a locating ring 15 and the distance between the upper end surface 16 of the locating ring and the shoulder 12 is slightly greater than the actual length of the piston 13 so that working chambers 17 and 18 are formed at opposite ends of the piston. The narrow clearance between the piston rod 2 and the body 1 is not sealed'from the chamber 17 so that hydraulic fluid from the chamber will act as lubricant in the clearance but fluid is prevented from escaping to the outside by an O ring 19 at the bottom end. Similarly fluid may pass into the clearance between the cylinder 5 and the sleeve 11 on the piston rod but is prevented from escaping at the upper end by an O ring 20. Leakage between the two cylinder chambers 17 and 18 across the piston is restricted by a piston ring 21.

Secured to the upper end of the cylinder 5 is a manifold disc 25 above which there is a chamber 26 defined by a cylindrical cover ring 27 and a top cover 28, the top cover being secured to the cylinder by a ring of tie bolts 29. Secured to the top of the top cover 28 are two triangular plates 31, 32 stiffened by triangular webs 33. The plates 31 and 32 have holes 34 through which a shackle pin 35 may be passed. The pile driver may be suspended from a crane by means of the shackle pin.

An inlet standpipe 40 passes through the top cover 28 to a connection 41 on the manifold disc 25 where it leads to an inlet passage 42 which passes to a servovalve 43 which is bolted to the manifold disc 25 by bolts 44. Branching from the passage 42 is a connection 45 leading to a gas-loaded hydraulic accummulator 46. There is a similar drain passage 47 leading from the servovalve to an outlet standpipe 48, the drain passage 47 having a branch 49 leading to a gas-loaded hydraulic accummulator 50.

A passage 52 in the manifold disc 25 interconnects an external port of the servovalve to a passage 53 in the cylinder which leads to a port 54 opening into the working chamber 17. Another passage 55 in the manifold disc 25 leads from another external port of the servovalve to a passage 56 in the cylinder 5 leading to a port 57 opening into the working chamber 18.

In use, the foot 3 is secured by the bolts 4 to the head of a pile and the pile driver is suspended with the pile vertically from a crane. The tubes 40 and 48 are connected by flexible hoses to a source of high pressure hydraulic fluid and a drain tank respectively. Through the servovalve one of the working chambers 17 and 18 is connected to the source and the other to drain to move the piston 13 in the cylinder 5 a short distance along the cylinder in one direction relative to the cylinder whereupon the connections through the servovalve are reversed to move the piston in the opposite direction. This reversal occurs at frequent intervals to produce a reciprocation of the piston relative to the cylinder of a frequency of between 25 and 150 cycles per second, for example 50 cycles per second. Although the frequency is high, the stroke is low, probably less than 3 mm. although the overall length of the pile driver may be 6 feet (2 meters) or more.

The servovalve is shown diametrically in FIG. 3 and will be seen to consist of a main valve 60 which is controlled by a pilot valve 61 which in turn is controlled by a torque motor 62. The main valve 60 has an inlet port 63 which is connected to the inlet passage 42 and leads to a chamber at the center of a spool 64. Output ports 65 and 66 are connected to the passages 52 and 55 respectively in the manifold disc while a drain port 67 is connected to the outlet passage 47. The pilot valve 61 consists of two spools 68 and 69 which are normally centrally positioned. The left-hand end of the spool 64 of the main valve has its area reduced by a spindle 70 and is connected by a passage 71 through a reducing valve 72 to the inlet passage 42. The right-hand end of the spool 64 is connected by a passage 73 to a chamber 74 the pressure in which is controlled by the spools 68 and 69, the spool 68 being connected by a passage 75 to the drain port 67 and the spool 69 being connected by a passage 76 to the pressurized fluid supply in the passage 71. If the torque motor 62 moves the spools upwardly as shown in the drawing, the right-hand end of the main valve is connected to pressurized fluid supplied through the passage 76 thus causing the main valve to move to the left, whereas if the pilot valve is moved downwardly as seen in the drawing the right-hand end of the main spool 64 is connected to drain through the passage 75 thus causing the main spool 64 to move the right. The position of the main valve spool 64 is sensed by an induction transducer 77 while the position of the pilot valve spools 68 and 69 is sensed by a transducer 78.

The control system by which the position of the torque motor 62 is adjusted is shown in block diagram form in FIG. 4 which shows the main valve 60, the pilot valve 61, the two position transducers 77 and 78 and the torque motor 62.

Referring now to FIG. 1 it will be seen that between the manifold disc 25 and the upper portion 7 of the piston rod 2 there is a chamber 81. This contains an electrical inductiontype position transducer 82 the main part of which is secured to the manifold disc 25 and the plunger 83 of which is secured to the piston rod. Returning now to FIG. 4, the signal output of the transducer 82 is supplied to a comparator-amplifier-control unit 84 where it is compared with an input from a ramp waveform generator 85. The control unit 84 produces a command signal in dependence upon its comparison and this signal is delivered along a signal line 86 to form the input to a control unit 87 where it is compared with inputs from the valve position transducers 77 and 78 supplied along signal lines 88 and 89 respectively. The control unit 87 produces an output signal which is delivered along a line 90 to the torque motor 62. The control system thus forms a closed loop whereby the piston of the pile driver is caused to move relative to the cylinder in accordance with the instructions supplied by the waveform generator 85, a subsidiary servo loop being constituted by the pilot valve 61, the main valve 60 and the control unit 87.

By causing the waveform generator to produce an appropriately shaped signal the main piston may be caused to accelerate more rapidly in one direction of its reciprocation than in the other. Thus when the pile driver is being used for driving a pile the downward acceleration will be the greater whereas the reverse will be the case when the pile driver is being used for extraction. A typical waveform is indicated in the block 85 in FIG. 4.

In the arrangement shown in FIG. 5 the piston rod 91 carries two pistons 92 and 93. In this case the valve 94 functions as a distributor valve and when the piston is to be moved downwardly hydraulic fluid pressure is admitted to the working chambers 95 and 96 above both pistons 92, 93 whereas when the piston is to be moved upwardly fluid pressure is admitted only to the cylinder chamber 97 below the lower piston and the chamber 98 below the upper piston is directly connected by the servovalve 94 to the cylinder chamber 95 above the upper piston so that there is a direct transfer of fluid and so force is exerted on the upper piston. Accordingly acceleration is greater in the downward direction of travel of the piston than in the upward direction. This distribution will be reversed when the driver is used for extraction. Clearly a greater number of pistons than two may be employed and the way in which pressure is applied to these may be varied depending upon whether the pile driver is being used for driving or for extraction. Moreover a control system having an externally applied waveform similar to that described in relation to FIGS. 1 to 4 may be used with a pile driver having a plurality of piston areas.

What we claim as our invention and desire to secure by Letters Patent is:

l. Vibratory pile driving apparatus including a motor ar'- ranged to impart to a pile forces of non-symmetric waveform wherein the motor comprises a double acting hydraulic cylinder and ram assembly, one of the two moving elements having means of connection to a pile, valve means for controlling the flow of pressurized working fluid to and from the working chamber and a waveform generator for supplying a control signal continuously to adjust the valve means so that fluid flows to and from said assembly to produce an acceleration to said ram in one direction relative to said cylinder which is greater than in the opposite direction.

2. Apparatus as claimed in claim 1 in which the piston has surfaces of equal area facing in the opposite directions and the valve means is arranged to supply fluid to the areas facing in opposite directions at different rates.

3. Apparatus as claimed in claim 2 which includes means for comparing said control signal with a measured value signal representing a quantity dependent on the supply of fluid and for adjusting the supply of fluid in dependence upon the comparison.

4. Apparatus as claimed in claim 3 which includes a transducer for determining the relative positions of the ram and cylinder and supplying the measured value signal in dependence on such determination.

5. Vibratory pile-driving apparatus comprising a double acting hydraulic cylinder-and-ram assembly, one of the two moving elements of the assembly having means of connection to a pile, a servovalve for controlling the supply of pressurised working fluid to and from the working chambers of the assembly, actuating means for the servovalve, and a closed loop control system comprising a position transducer arranged to provide a measured value signal representing the instantaneous position of the ram relative to the cylinder, means for supplying an input signal of asymmetric waveform, means for comparing the measured value signal with the input signal and for delivering a command signal dependent upon the deviation and identical series of surfaces facing in the opposite direction, one of the two moving elements of the assembly having means of connection to the pile, the motor means being arranged in reciprocate the mass relative to the pile longitudinally thereof and to impart vibratory forces to the pile,

the motor means being arranged to impart, or being adjustable to impart, to the pile forces of non-symmetrical waveform, and valve means for controlling the supply of pressurized working fluid to and from the working chamber of the assembly, the valve means being arranged to supply fluid to a number of the first series of surfaces for movement of the piston in one direction and to a different number of the second series for movement of the piston in the opposite direction so that the acceleration of the movement of the piston in one direction relative to the cylinder is, or can be caused to be, greater than in the opposite direction.

' e e s e e 

1. Vibratory pile driving apparatus including a motor arranged to impart to a pile forces of non-symmetric waveform wherein the motor comprises a double acting hydraulic cylinder and ram assembly, one of the two moving elements having means of connection to a pile, valve means for controlling the flow of pressurized working fluid to and from the working chamber and a waveform generator for supplying a control signal continuously to adjust the valve means so that fluid flows to and from said assembly to produce an acceleration to said ram in one direction relative to said cylinder which is greater than in the opposite direction.
 2. Apparatus as claimed in claim 1 in which the piston has surfaces of equal area facing in the opposite directions and the valve means is arranged to supply fluid to the areas facing in opposite directions at different rates.
 3. Apparatus as claimed in claim 2 which includes means for comparing said control signal with a measured value signal representing a quantity dependent on the supply of fluid and for adjusting the supply of fluid in dependence upon the comparison.
 4. Apparatus as claimed in claim 3 which includes a transducer for determining the relative positions of the ram and cylinder and supplying the measured value signal in dependence on such determination.
 5. Vibratory pile-driving apparatus comprising a double acting hydraulic cylinder-and-ram assembly, one of the two moving elements of the assembly having means of connection to a pile, a servovalve for controlling the supply of pressurised working fluid to and from the working chambers of the assembly, actuating means for the servovalve, and a closed loop control system comprising a position transducer arranged to provide a measured value signal representing the instantaneous position of the ram relative to the cylinder, means for supplying an input signal of asymmetric waveform, means for comparing the measured value signal with the input signal and for delivering a command signal dependent upon the deviation determined by the comparison, and means for supplying the command signal to the actuating means.
 6. Vibratory pile-driving apparatus comprising a mass adapted to be connected to a pile and to be movable longitudinally thereof and motor means comprising a double acting hydraulic cylinder-and-piston ram assembly, the piston having a first series of surfaces facing in one direction and a second and identical series of surfaces facing in the opposite direction, one of the two moving elements of the assembly having means of connection to the pile, the motor means being arranged in reciprocate the mass relative to the pile longitudinally thereof and to impart vibratory forces to the pile, the motor means being arranged to impart, or being adjustable to impart, to the pile forces of non-symmetrical waveform, and valve means for controlling the supply of pressurized working fluid to and from the working chamber of the assembly, the valve means being arranged to supply fluid to a number of the first series of surfaces for movement of the piston in one direction and to a different number of the second series for movement of the piston in the opposite direction so that the acceleration of the movement of the piston in one direction relative to the cylinder is, or can be caused to be, greater than in the opposite direction. 